This invention relates to a process for separating, specifically in multiple stages, acid components such as CO.sub.2, HCN and specifically H.sub.2 S from gases, specifically coke oven gases, by means of ammonia recirculation scrubbing wherein the ammonia which during scrubbing has been bound to the acid components is released by a deacidification treatment and recirculated to the scrubbing process at least in part as substantially pure liquid ammonia.
It is known in the art to separate the acid components of a gas with a suitable eluant and then separate the adsorbed acid components by suitable means from the eluant. Ammonia eluting for stripping H.sub.2 S from gases containing up to about 1.0 to 1.5 g H.sub.2 S/m.sup.3 under normal conditions is state of the art. Recently, a number of improvements have been suggested. For example, German patent document 20 56 727 disclosed a process in which both gaseous and dissolved ammonia are used for hydrogen sulfide scrubbing. In addition, numerous attempts have already been made at increasing the ammonia content of the wash water in the deacidification stage, e.g., as disclosed in German patent publication 1,107,882; or to subdivide the separation process into several stages, using first an ammonia water with a higher ammonia concentration and, in the second stage, an ammonia water of customary concentration as shown in German patent publication 1,091,273. Also known from German patent publication 1,085,641 is the separate use of ammonia gas containing hydrogen sulfide, for one, and of pure ammonia gas obtained from ammonia salts or other sources, in a hydrogen sulfide scrubber. While these and many other patents disclose separate treatment of the gases to be stripped of acid components, and specifically of H.sub.2 S, and specifically in coke oven gas by means of ammonia scrubbing, either ammonia eluants or gaseous ammonia are employed.
Due to present environmental regulations, it is necessary to reduce especially the H.sub.2 S content in the purified gas. In order to meet these regulations with the aid of ammonia separation, ammonia must be recirculated to the process at least in the scrubbing of coke oven gas, since the natural ratio of NH.sub.3 to H.sub.2 S in the coke oven gas does not permit an extensive separation of the H.sub.2 S. Normally, the ammonia is recirculated into the separation process by way of a so-called deacidifier. As its name implies, the deacidifier is used to remove the acid components from the ammonia eluant and retain the ammonia. For reasons of equilibrium, however, in this process part of the acid component remains in the eluant solution. This leads to two essential disadvantages of such a procedure. First, because of the residual content of acid components, only about 80% of the ammonia contained in the eluant solution is available for scrubbing. Second, and more aggravating, the partial pressure of the acid components, especially of the H.sub.2 S, above the deacidified eluant solution prevents the H.sub.2 S separation down to the presently specified values.